You can conveniently recharge your prepaid mobile online directly using your ICICI or HDFC bank account at

http://www.icicibank.com/Personal-Banking/onlineservice/online-services/PrepaidMobileRecharge/prepaid-mobile-recharge.html

http://www.hdfcbank.com/personal/payments/prepaid_refill/pre_refill.htm

It is available for
Operator Name     / Circle
Airtel – Andhra Pradesh, Bihar, Chennai, Delhi, Gujarat, Karnataka, Kerala, Madhya Pradesh, Mumbai,Maharashtra,Rajasthan, Tamil Nadu, Uttar Pradesh (East),Uttar Pradesh (West), West Bengal

BPL – Mumbai

Vodafone -  Andhra Pradesh, Chennai, Delhi, Gujarat, Haryana, Karnataka,Kerala, Kolkata, Maharashtra,Mumbai, Punjab, Rajasthan,Tamil Nadu, Uttar Pradesh (East), Uttar Pradesh (West), West Bengal

Idea – Andhra Pradesh, Delhi, Goa, Gujarat, Haryana, Himachal Pradesh, Kerala, Madhya Pradesh, Maharashtra,Rajasthan, Uttar Pradesh (East), Uttar Pradesh (West)

Reliance India Mobile – All India

Tata Indicom – All India

Aircel – Tamil Nadu

BSNL – Andhra Pradesh, Chennai, Gujarat, Haryana, Karnataka, MP & Chattisgarh, Punjab, Rajasthan. Tamilnadu, Uttar Pradesh (East & West), Maharashtra

Recharge Limit per mobile number per day – Rs 1,000

Recharge amounts are:
Airtel – 50, 99, 100, 200, 300, 333, 444, 500, 1000 (fixed denominations)
Aircel – 50 to 10,000 (flexi recharge)
BSNL – 55 to 6,000 (flexi recharge)
Reliance GSM – 500, 400, 300, 299, 285, 201, 200, 199, 145, 110, 105, 100, 75, 60, 50, 40, 30, 25, 20, 10
Reliance CDMA – 50 to 10,000 (flexi recharge)
Loop – 50 – 10,000 (flexi recharge)
TATA – 50 to 10,000 (flexi recharge)
Virgin – 50 to 10,000 (flexi recharge)
Vodafone – 50 to 10,000 (flexi recharge)

* Please note: All flexi recharges are subject to availability of the recharge plan with the mobile operators during the transaction period. Request you to please confirm the plan details with your respective mobile operator before entering the denomination

Some of the amounts are top up for lifetime validity prepaid mobile accounts, others are  valid for 30 days.